{905}_The Central Capsule_ of the #Plectoidea# constantly exhibits the peculiar characters of the MONOPYLEA or NASSELLARIA. It is commonly ovate, more rarely ellipsoidal or even spherical, sometimes conical or lentelliptical. The lower or basal pole of its vertical main axis constantly exhibits the characteristic "porochora" (or the area porosa) of the MONOPYLEA, and upon this rests the peculiar "podoconus" (or the pseudopodial-cone) of this legion. On this porochora the central capsule is in immediate connection with the central point of the skeleton, or the horizontal common central rod, from which the radial spines arise. The endoplasm, or the protoplasm of the central capsule (besides the podoconus), contains commonly one large alveole or several small vacuoles, and often pigment-granules. The nucleus is large, spherical or ovate, and exhibits the same character as in all the other MONOPYLEA; it encloses usually a single nucleolus. The position of the central capsule and its topographical relation to the skeleton offers in the different #Plectoidea# some important and as yet unsolved problems, which can be answered only by fresh and accurate observations on living specimens. In _Triplagia_ and _Triplecta_, where the triangular skeleton lies in a horizontal plane, the vertical main axis of the central capsule is perpendicular to the central point of that supporting triangle. In _Plagiacantha_ and _Plectophora_, where the three radial spines correspond to the edges of a flat pyramid, the capsule is enclosed in the pyramidal space of the latter, its basal pole touching the apex; therefore in the normal position of the body the three divergent rays are directed upwards. In _Tetraplagia_ and _Tetraplecta_ probably the same position is retained, and therefore the fourth free spine, here developed, is probably directed vertically downwards. In _Plagoniscus_ and _Plectaniscus_, however, and moreover, in the closely allied _Plagiocarpa_ and the corresponding _Periplecta_ (Pl. 91, figs. 5, 10) the position of the central capsule, relative to the skeleton, seems to be inverse, and to agree with that of the #Stephoidea# (_Cortina_, _Cortiniscus_, &c.) and the #Cyrtoidea# (_Pteroscenium_, _Clathrocorys_, &c.); the three divergent spines are here directed downwards (as basal feet), whilst the opposite fourth spine is vertically directed upwards (as an apical horn); the capsule rests here upon the tripod, which lies below it, and is inclined with its dorsal face to the apical spine. In the majority of the other #Plectoidea# the position of the central capsule and its relation to the skeleton are not yet sufficiently observed, and require further accurate researches. Its position seems to be very different in the several genera. The capsule is never perforated by parts of the skeleton; this latter is constantly extra-capsular.